Electric motors of a certain construction type are as a rule cooled by a through-ventilation. In this respect, both self-ventilation with an impeller seated on a shaft of the electric motor and external ventilation with a separately driven and supplied fan can be implemented. The cooling by the coolant flow used for the cooling can be variably configured by the design of the electric machine and of the associated component, such as the wheel drive, to be driven. In this respect, as a rule, air or an air flow is used as the coolant, with other cooling gases or cooling fluids also generally being able to be considered.
In the case of electric motors for wheel drives of work machines such as construction machinery and/or mining machinery, for example in the form of trucks, dump trucks or mining devices, the through-ventilation of the electric wheel motors is implemented in two different manners in dependence on the design.
It has already been proposed, on the one hand, to introduce a cold air flow into the so-called axle box of the rear wheel drive of the dump truck, wherein the cold air flow flows along the stator and/or housing to the wheel side of the electric motor. The air enters through the openings in the wheel-side bearing plate into the interior of the motor, is divided between the bores in the stator and in the rotor and the air gap between the stator and the rotor and flows to the side remote from the wheel. The heated air there flows through openings in the bearing plate of the electric motor remote from the wheel.
The main problem in this embodiment in connection with drives for construction machinery or mining machinery such as dump trucks is the open design of the bearing plate at the wheel side. The transmission of the wheel drive, which is typically lubricated and cooled by oil, is typically installed behind the end face of the electric motor at the wheel side. If, however, leaks in the oil circuit or at the drive shaft seal occur here, the electric motor is contaminated by transmission oil. Oil droplets and also other contaminants are entrained into the inner space of the electric motor by the coolant flow which enters through the bearing plate at the transmission side into the interior of the electric motor. The contamination of the motor which has taken place sets it into a state which is typically irreparable, whereby simple damage in the oil circuit can bring about the complete failure of the electric drive component.
On the other hand, designs of electric motors are known in which the cooling air is supplied to the electric motor from the outer periphery in an almost central manner, i.e. at the center of the motor housing, and is expelled again over the bearing plates after deflections in the interior of the electric machine at both ends at the end side, cf. e.g. DE 103 17 593 A1. The electric motor can hereby admittedly be protected against the penetration of oil and other contaminant substances, but requires a housing which is used for the dividing of air. However, this increases the outer diameter and also the weight of the electric motor so that the electric motor is at least not usable for wheel drives of smaller work machines for space reasons and increases the unsprung masses noticeably so that such designs of electric motors can primarily be used for very large dump trucks.
Starting from this, it is the underlying object of the present invention to provide an improved drive apparatus of the initially named type which avoids disadvantages of the prior art and further develops the latter in an advantageous manner. A sufficient cooling should in particular be achieved without problems of contamination for the inner motor space and with a spatially compact design of the electric motor which is of lightweight construction such that the drive can also be used as a wheel drive for smaller dump trucks and similar construction machinery or mining machinery.
The named object is achieved in accordance with the invention by a drive apparatus for a wheel of a work machine, comprising: an electric motor with a rotor which is rotatably received in a stator, the rotor supported at bearing plates arranged at end sides and in which two coil head spaces are provided which are bounded by the stator, by the rotor, by a shaft of the electric motor and by the bearing plates or by a bearing plate, wherein a cooling apparatus for cooling the stator and the rotor comprises at least one coolant path through the coil head spaces which is supplied with coolant via a coolant inlet, wherein the cooling apparatus comprises a space surrounding the stator, and which is bounded at an outer peripheral side by a housing part spaced apart from the stator and having the coolant inlet, wherein the space communicates via communication openings provided at the ends of the stator with the coil head spaces, with one bearing plate being closed and free of a coolant passage and with the other bearing plate or the stator having at least one coolant outlet at the end of the motor at a side of the bearing plate such that coolant is conducted via the coolant inlet into the space, the coolant further conducted in the space propagating over an outer peripheral side of the stator, wherein the coolant is introduced through the communication openings into the coil head spaces and is drained through the at least one coolant outlet.
It is proposed in accordance with an advantageous embodiment of the present invention to cool the stator and its stator winding from an external peripheral side of the stator and, for this purpose, to utilize a space present about the electric motor or its stator for the installation environment of the electric motor such that the cooling air flow can also flow over the outer peripheral side of the stator. The coolant introduced into the inner motor space can flow out at an end side of the electric motor again via only one bearing plate, whereas the other bearing plate which preferably faces a transmission can be configured as closed. The space surrounding the stator is advantageously bounded at the outer peripheral side by a housing part which is spaced apart from the stator and in which the coolant inlet at the peripheral side is formed and can communicate at the inward peripheral side with the coil head space via communication openings which are provided at the ends of the stators in the bearing plates. With such an embodiment of the electric motor, the coolant can advantageously flow into the named space from a peripheral side via the coolant inlet, can be distributed there and can flow over the outer peripheral side of the stator to cool the stator and can flow through the communication openings into the coil head spaces in the interior of the electric motor to cool the rotor and the coil heads and can finally exit at the coolant outlet in the named one bearing plate.
An oil contamination of the inner motor space at the end side can be avoided by such a through-ventilation, but a sufficient cooling can simultaneously also in particular be achieved at the stator, with radial construction space being utilized or saved in the best possible manner by the utilization of a space which is already present per se about the electric motor toward the installation environment such that the drive apparatus is overall also suitable for smaller wheel drives at lighter dump trucks.
The coolant entering into one of the coil head spaces can in particular flow through bores or passages in the rotor and/or through the air gap between the stator and the rotor from the named coil head space at the side of the closed bearing plate into the coil head space having the at least one coolant outlet.
In an advantageous further development of the invention, the electric motor can itself be configured as without a housing, with the housing part bounding the named space at the outer peripheral side being able to be formed by a structural part of the installation environment of the electric motor. Depending on the installation situation of the electric motor, the named structural part can have different configurations, with the named structural part, however, not primarily serving the casing of the electric motor, but rather satisfying a different main functional purpose and already being present per se due to this other main purpose, for example for supporting the assembly to be driven by the electric motor.
On a use of the electric motor in a wheel drive of, for example, a dump truck, the named structural part can be an axial part of the wheel axle of the wheel which is driven by the electric motor, with the electric motor being received in the named axial part of the electric motor. If the electric motor is used for driving a tracked chassis, the named structural part can likewise be an axial part in which the electric motor is arranged, with the axial part being able to be associated in this case with a drive pinion or with the sprocket of the chain.
With the named casing-less design of the electric motor, the outer peripheral surface of the stator can in particular be arranged in an exposed manner with respect to the named space and can bound the inner periphery of the named space. The stator metal sheet stack and/or a stator winding arranged at the stator metal sheet stack can be adjacent in an at least partially exposed manner to the named space such that the cooling air can sweep directly over the stator in the space between the installation environment of the electric motor and the stator metal sheets or stator windings.
Furthermore, in an advantageous embodiment of the invention, the electric motor can be installed and fastened, without any interposition of a separate housing, via a stator end ring provided at a stator end and/or via the bearing plate connected thereto directly at the structural part of the installation environment, in particular the wheel axle housing. In a further development of the invention, the named stator end ring, which is arranged at the end side at the stator of the electric motor, can form a unit with the stator metal sheet stack having the stator winding and can have fastening points by means of which the electric motor is fastened to the named structural part. The named stator end ring can, for example, project a little beyond the stator metal sheet transversely to the axis of rotation of the electric motor and can have the named fastening points at the protruding collar section, for example in the form of axial passage bores which allow an axial screwing tight at the wheel to be driven or at a wheel axial part connected thereto.
To increase the cooling effect of the air flow flowing onto the stator through the aforesaid space, the stator can have, in an advantageous further development of the invention, cooling ribs at the outer periphery which project into the named space. The named cooling ribs can, for example, be formed by cut-outs or milled-out portions in the stator metal sheet stack. The aforesaid communication openings, through which the space communicates with the inner motor space or with the coil head spaces, can have different surfaces on the different sides of the stator or can be configured with different sizes in a further development of the invention, with the at least one communication opening advantageously being formed as larger at the side of the closed bearing plate than the at least one communication opening at the side of the other bearing plate. If a plurality of communication openings are provided at each side of the stator, all the communication openings, which are provided at one stator side, in particular at the side of the closed bearing plate, can together have a larger surface—viewed in total—than the other communication openings which are provided at the other side of the stator at the other bearing plate.
The named communication openings can in this respect in particular be configured as passing through the stator or the stator metal sheets such that the inner motor space or the coil head spaces communicate with the outwardly disposed space transversely to the axis of rotation of the electric motor.
The dimensional design of the named communication openings is in this respect in particular made such that more coolant flows into the inner motor space at the side of the closed bearing plate than at the side of the other bearing plate in which the coolant outlet is provided. The dimensional design of the passage openings can in this respect in particular be made such that around twice as much coolant flows into the Inner motor space or into the coil head space at the side of the closed bearing plate than at the side of the bearing plate having the coolant outlet.
To sufficiently cool the rotor in the interior of the electric motor, the named rotor can be provided with coolant passages or coolant bores through which the coolant can flow from the side of the closed bearing plate to the bearing plate having the coolant outlet opening.
The coolant supply via the aforesaid coolant inlet can generally take place at a different point of the named space, with the coolant inlet advantageously being able to be arranged at the peripheral side to be able to introduce coolant into the cooling space surrounding the stator from a peripheral side. The named coolant inlet can in this respect be arranged spaced apart from the axial end sections of the named space in a middle spatial section. In this respect, an exactly central arrangement of the coolant inlet can be provided at fifty percent of the length of the axial space. In an alternative, advantageous embodiment of the invention, the coolant inlet can be displaced from the named center a little toward the bearing plate which has the coolant outlet opening, for example arranged at approximately a third of the axial length of the space—starting from the bearing plate having the coolant outlet.
The named coolant inlet is advantageously arranged at an upper side of the named structural part.
The space which can be flowed through by the coolant and which surrounds the stator can be of different designs; it can, for example, only surround a part of the stator or can only extend along a sector of the stator. In an advantageous further development of the invention, the named space can form an annular space which surrounds the stator at all sides.
The electric motor can be connected to the wheel of the work machine to be driven and to the interconnection of a transmission to convert the speed of the motor shaft in the desired manner or in the desired step-up/step-down ratio into the speed of the wheel to be driven. The transmission in this respect is advantageously seated at the side of the bearing plate formed as closed.
The invention will be explained in more detail in the following with reference to a preferred embodiment and to associated Figs.